1. Field of the Invention
The present invention relates to roll off container hoists, also called roll off hoists, and more particularly, directed toward a roll off container hoists accommodating low overhead clearance or obstructions, e.g. tree branches, wires, buildings and the like, will full roll off capabilities.
2. Background Information
In general, transportable containers are utilized for a great variety of materials including solid and liquid waste products. The containers are adapted to be picked up and set off by a transport vehicle such as a truck, or a trailer for larger containers, with a suitable lift device known as a “roll-off hoist” or a “roll off container hoist”.
Containers for freight, bulk materials, and other products come in numerous sizes and load capacities. Open Top Containers are generally available from about 10 Cubic Yard to 60 Cubic Yard capacity depending on the individual need. Containers typically have a ¼″ floor or 3/16″ floor. Side material ranges from 12 gauge to 3/16″. Containers can have conventional side stake style sides or “T” sidewall style that eliminates side posts.
It has been a common practice to pull each container, regardless of its size and loading, aboard the transport vehicle with its forward end abutting a fixed stop on the vehicle. It has been proposed that with such a system, the center of gravity of the container may often be located in an unfavorable position on the transport vehicle, imposing unnecessarily high loading upon a weaker area of the vehicle frame and imparting unnecessarily heavy loading to the hoist during loading and unloading of the hoist. Additionally the conventional roll off container hoist designs do not accommodate normal operation in height restricted areas.
U.S. Pat. No. 5,088,875 addressed the problem of designing a hoist to accommodate very large containers that create undesirable stress problems. The solution provided was a more complicated and costlier frame design. Specifically the roll-off hoist of the '875 patent included a trailer main frame, a roll-off hoist frame hingedly connected to the rearward end of the main frame with the hoist frame defining a second pair of tracks which align with the first pair of tracks when the hoist frame is in the horizontal transport position, and a trolley mounted to slide within the first and second pair of tracks, and actuator means interposed between the trolley and the hoist frame for moving the trolley within the first and second pairs of tracks and moving a container connected to the trolley forwardly of the hoist frame.
The '875 patent included structure to prevent the trolley, or carriage, from being extended until the hoist frame was in the horizontal position. The structure incorporated several separate hydraulic circuits to accommodate the various separately movable components, and a system to prevent the premature movement of the trolley. The hoist of the '875 patent did not provide full functioning roll off capabilities. Specifically, the trolley could not be extended in the elevated condition, the trolley could not absorb the loading in the elevated condition, a separate hydraulic mechanism is required for moving the trolley and a separate stopping mechanism is required to prevent the premature moving of the trolley. Finally the '875 patent is essentially limited to trailer applications.
Other roll off hoist designs are disclosed in U.S. Pat. Nos. 6,332,746, 6,068,440, 5,088,875, 4,986,719, 4,934,898, 4,840,186, and 4,529,349 which together with the '875 patent are incorporated herein by reference.